JP2959025B2 - Ni-plated steel sheet for can and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a material for cans in which seams of a can body are seamed by welding when making cans such as food cans, and various materials required as materials for cans such as corrosion resistance and weldability after painting. It relates to a Ni-plated steel sheet for welded cans having particularly excellent pitting corrosion resistance in addition to its properties.

[Prior Art] Ni-plated steel sheet is one of the materials currently used for cans. Ni is a metal with good corrosion resistance, and also has the required processing characteristics and weldability for can materials.

Many can bodies, such as food cans, are made by rolling a square can material and seaming both ends, and soldering, welding, bonding, and the like are used for this seam. Soldering is used only for Sn-plated steel sheets, and the welding method and the bonding method are methods that have recently been used.However, when comparing the two methods, the welding method is superior in various aspects, and organic materials are used. In the conventional bonding method, the adhesive has a limitation in heat resistance and a reduction in productivity due to the bonding time, and is limited in use and process. In the welding method, electric resistance heating welding is performed while sandwiching a seam portion between copper wire electrodes and pressing with a roll. At this time, for example, in the case of a Cr-plated steel sheet, the hardness of the coating surface is large, the area covered with the oxide or hydroxide of Cr is large, and the actual contact area is smaller than the apparent contact area. For this reason, the contact electric resistance between the joint surfaces increases, and a high voltage must be applied to obtain a desired welding current. When a high voltage is applied, the current flows locally and a splash called dust is generated in this local area, so that a good weld surface cannot be obtained. Ni-plated steel sheets to which this welding method can be applied are suitable for can materials.
For example, JP-A-36-15252 proposes a Ni-plated steel sheet in which Ni is plated at 0.02 to 0.3 μm. Recently, proposals have been made to improve corrosion resistance and weldability.
In JP-A-62-139898, 10 mmg / m2 to ²⁰⁰ mmg / m
A surface-treated steel sheet is disclosed, which is plated with Cr of ² and further plated with Sn, Cu, or Ni of ²⁰ to 500 mmg / m ² in a state having locally convex portions thereon, and having a chromate layer in the upper layer again. ing.
In this method, corrosion resistance is ensured by the double plating layer, and defects in the weldability of Cr are compensated for by the upper plating layer.

[Problems to be Solved by the Invention] However, when the Ni plating layer is present, the electrode potential of Ni is much more noble than the electrode potential of Fe, and Fe is very easily eluted by contact electrolytic corrosion. This phenomenon is particularly severe in the case of vegetable juices and meats containing salt in the contents of the can, and the can may be perforated. JP-A-62-139898
As described above, if a Cr plating layer exists between the Ni plating layer and the steel substrate, the potential gradient is alleviated and the tendency is slightly improved, but with this film configuration, the Cr plating layer cracks when it is processed. Occurs and the steel at the tip is exposed. For this reason, the corrosion resistance after processing required for the material for cans is insufficient, and there remains a problem that pitting corrosion cannot be prevented.

In order to solve this problem, the present invention has been made, and aims to provide a steel plate for a welding can having excellent corrosion resistance and pitting corrosion resistance together with various properties as a material for a can, such as weldability. is there.

[Means for solving the problem] The means for achieving this object is that the surface layer of the steel sheet is made of Cr.
In Ni thermal diffusion layer has a 0.05 g / m ² or more 1 g / m ² or less of the Ni plating layer on the diffusion layer, a welded steel sheet for cans having a chromate layer on the Ni plating layer, Preferably, Cr
The total amount of Cr and Ni in the Ni thermal diffusion layer is 0.02 g / m ² or more and 0.2 g / m ²
The following is a steel plate for a welding can that is the following, and preferably, a chromate layer is a steel plate for a welding can whose Cr conversion is 5 mmg / m ² or more and 30 mmg / m ² or less, and a method for producing such a welded steel plate. The steel sheet before heat treatment is coated with a Cr-Ni alloy, and when heat-treating the steel sheet, a heat-spreading layer of Cr / Ni is generated.After temper rolling, Ni plating is applied and then chromate treatment. A method of producing a steel sheet for a welding can, which is subjected to Cr plating on the surface of the steel sheet before heat treatment and then Ni plating. A method of manufacturing a steel plate for a welding can that is subjected to Ni plating and then subjected to a chromate treatment.The surface of the steel plate before heat treatment is subjected to Cr plating and then Ni / Fe alloy plating. Generate Ni heat diffusion layer, pass temper rolling, apply Ni plating, then chromate Method of manufacturing a welded steel sheet for cans subjected to physical is.

[Action] As is well known as a stainless steel, a Cr-Ni-Fe alloy generally has good corrosion resistance. Ni is also a metal with good corrosion resistance, but when it is used to protect steel, it is necessary to consider catalytic electrolytic corrosion. That is, when there is a plating layer having a noble potential with respect to steel, such as Ni, not only cracks during processing, but also through film defects such as pinholes,
In the presence of an electrolyte, as in the inner surface of a food can, a steel base and a battery are formed, and the elution of base steel is promoted, and the steel base is deeply eroded. The amount of this elution is proportional to the potential gradient, but the potential series is Ni, CrNi alloy, Cr, and Fe in the order of noble. Suppress elution. Even if the Cr plating layer is not diffused, its potential is located between steel and Ni.
・ It does not relax continuously like the Ni thermal diffusion layer. The effect of continuous relaxation is particularly remarkable where cracks and pinholes are present.

Furthermore, if a Cr / Ni heat diffusion layer is present, good corrosion resistance can be maintained after processing in addition to general corrosion resistance.
When a thin plating layer is subjected to severe processing such as winding processing, cracks occur in the plating film. In this case, if it is a Cr / Ni diffusion layer, Cr and Ni are diffused deep into the thermal diffusion layer, and even if a crack occurs at the upper part of the layer, the Cr or Ni still remains under the crack.
Prevents the presence of steel. For this reason, the elution of Fe is suppressed and the corrosion resistance is maintained even after the winding process at the time of can making.

However, the use of only the Cr / Ni thermal diffusion layer is not satisfactory for weldability. Cr has a high affinity for oxygen, and oxides or hydroxides having insulating properties are easily generated. For this reason, the Cr / Ni diffusion layer has a disadvantage that the contact electric resistance of the welded surface is large and a good welded surface cannot be obtained. On this Cr / Ni diffusion layer
The presence of the Ni plating layer makes up for this disadvantage. In addition, Ni
Is a metal having good corrosion resistance, and further has a very high corrosion resistance. Has the effect be Ni plating layer is thin, to offset ensures the weldability disadvantages of Cr · Ni thermal diffusion layer is required thickness of 0.05 g / m ^2, also exceed 1 g / m ² Even if it is thick, its effect does not change much and it is a considerably expensive metal. Therefore, an upper limit of 1 g / m ² is appropriate.

The chromate layer on the Ni plating layer improves the adhesion of the paint, and may be a chromate layer generally used for Sn-plated steel sheets. However, in order to ensure the adhesion of the paint, it is desirable that the Cr content is 5 mmg / m ² or more, and if too large, the weldability may be impaired.
Desirably, it is 30 mmg / m ² or less.

While effects on the corrosion resistance after processing of cr · Ni diffusion layer appears the amount of about 0.01 g / m ^2, in consideration of the variation in practical working conditions, in order to reliably maintain the corrosion resistance after the tightening process Is desirably 0.02 g / m ² or more.
Regarding the corrosion resistance, the thicker the Cr / Ni thermal diffusion layer is, the better. However, in order to satisfy the under-coat corrosion resistance required for cans,
It is not necessary to exceed 0.2 g / m ² , and considering economics,
The amount is desirably 0.2 g / m ² or less.

In order to manufacture the above steel plate for welding cans, first, Cr / Ni
It is necessary to form a thermal diffusion layer. For this, if Cr and Ni are attached to the surface of the steel sheet before the heat treatment, Cr and Ni are thermally diffused when the steel sheet is heat-treated. This method is more economical than plating a steel sheet whose mechanical properties have been adjusted by heat treatment and temper rolling, as in the case of general plating, and the effect of the second heat treatment. You don't have to. There are many methods for depositing Cr and Ni, but when Cr and Ni are plated with an alloy, the ratio of Cr and Ni in the thermal diffusion layer does not fluctuate much, and the ratio can be easily controlled. Instead of performing Cr / Ni alloy plating, Ni may be plated after plating Cr. In this case, the plating step is increased by one, but the ratio of Ni to Cr is higher in the upper part of the diffusion layer than in the deep part, the upper part is closer to the potential of Ni, and the deep part has an increase in the Fe content. Since the potential becomes closer to the potential of Fe, the potential gradient between the dissimilar metals is alleviated more continuously. Also, if Ni / Cr alloy plating is performed after Cr plating, the Cr concentration in the deep portion of the diffusion layer is ensured, and copper at the crack tip is more reliably protected.

In addition to these plating methods, for example, Cr plating,
If Ni plating is performed followed by Fe plating, the Cr concentration in the deep part of the diffusion layer is also ensured, and if heat treatment is performed after applying Cr, Ni, Fe alloy plating, the heat treatment temperature is low and the time is short Even in this case, a sufficiently diffused layer is obtained. Also, Cr ・ Fe
The heat treatment may be performed after the Ni / Fe alloy plating is performed following the alloy plating. These adhesion methods may be selected in consideration of the use of the material for the can, the sheet thickness, the annealing conditions, and the like.

The steps of undergoing heat treatment in the step of adjusting a steel sheet include an annealing step after cold rolling and an overaging step, and in the latter, only a part of the material is subjected to the treatment. The former is heated to around 700 ° C, and the latter is heated to around 500 ° C. Since Cr diffuses sufficiently in any of the heat treatments, either heat treatment step can be used.

When Ni plating is applied after temper rolling, the contact area can be increased at the time of welding as described above, and even if a crack occurs in the Cr heat diffusion layer due to temper rolling, it can be covered. I can do it.

The chromate treatment is performed at the end of the process in order to secure the adhesion of the paint by the upper layer film again, and may be performed using a dichromic acid bath or a chromic acid bath as is generally performed.

[Example] (Example) After the surface of a cold-rolled steel sheet is plated with Cr and Ni with varying amounts of adhesion, heat-treated, and subjected to temper rolling at an elongation of 2%,
Ni was plated with a different adhesion amount, and a chromate treatment was performed thereon. Various characteristics of the corrosion resistance, paint adhesion and weldability required for the amount of can material were examined for these test pieces and the test piece according to the conventional example which was not subjected to a heat treatment after Cr plating.

 The plating and chromate conditions were as follows.

Cr plating: CrO ₃ 200 g / (NH ₄ ) F 3 g / Bath temperature 50 ° C. Current density 40 A / dm ² Ni plating: NiSO ₄ .6H ₂ O 240 g / NiCl ₂ .6H ₂ O 45 g / H ₃ BO ₃ 30 g / bath temperature 45 ° C. pH 2.7 current density 10A / dm ² Ni · Fe alloy _{plating: NiSO 4 · 6H 2 O 240g} / NiCl 2 · 6H 2 O 45g / FeSO 4 · 7H 2 O 150g / H 3 BO 3 30g / bath temperature 50 ℃ pH 2.0 Current density 10A / dm ² Chromate treatment A: Na ₂ Cr ₂ O ₇ 20g / bath temperature 40 ℃ pH 5.5 Current density 5A / dm ² Chromate treatment B: CrO ₃ 20g / Na ₂ SO ₄ 0.6g / bath temperature 40 ° C pH 5.5 Current density 40A / dm ² Test Nos. 1, 3, 5, 7, 9, 11, 13, 15 and 17
About chromate treatment A, test Nos. 2, 4, 6,
8, 10, 14, and 16 were treated in the same B.

In Test Nos. 1, 4, 7, 10, and 13, Ni plating was performed after Cr plating, and a heat treatment was performed at 700 ° C. for 20 seconds.
For 5, 8, 11 and 14, 430 ° C with Cr / Ni alloy plating
Heat treatment for 10 hours and test Nos. 3, 6, 9, 12, and 15
Then, after Cr plating, Ni · Fe alloy plating was performed, and heat treatment was performed at 680 ° C. for 30 seconds.

As the corrosion resistance test, corrosion resistance after processing, corrosion resistance under coating,
An iron dissolution test and a pitting corrosion test were performed, a T-peel test was conducted as a paint adhesion test, and a contact electric resistance was examined for weldability.

Corrosion resistance after processing is to examine the corrosion resistance after winding processing at the time of can-making.
After being immersed in an aqueous solution containing 5% and 1.5% citric acid at 38 ° C. for 96 hours, iron rusting was examined. When folding in two, do not insert a spacer between them, so-called close-contact bending
OT, when a plate having the same thickness as the test piece is inserted, the T value is determined according to the bending method up to 1T and below 5T depending on which bending method did not cause rust. Here, 30 samples were tested, and the case where all were better than 1T was evaluated as ○, the case where 2T was mixed was evaluated as Δ, and the case where 3T was mixed was evaluated as x.

The iron dissolution test examines the corrosion resistance of the contents of cans such as fruits and juices. Paint the test material with an epoxy-based paint in a can (20 μm), bake at 205 ° C for 10 minutes, and then add 1.5% citric acid and sodium chloride. It was immersed in an aqueous solution containing 1.5% at 38 ° C. for 96 hours, and the amount of iron eluted in the immersion liquid was measured.

In the UCC test, the paint in the can is baked in the same way as the iron dissolution test, and then the coating is scratched with a knife to reach the base in a cross, and immersed under the same conditions as the iron dissolution test, and then the deterioration around the scratch The situation was observed. The deterioration was observed by visually observing the state of the coating film turning over and the state of corrosion of the substrate, and the state where no corrosion was observed was evaluated as ○, the state where corrosion was slightly observed but was practically acceptable, and the state where corrosion was observed at first glance It evaluated by x.

In the blister test, similarly to the iron dissolution test, a specimen in which a coating film in a can is baked is first heated to 120 ° C. in 0.1% salt and exposed to a pressure of ² kg / cm ² for 1.5 hours. After this, further 0.1
% Saline solution at 38 ° C. for 96 hours, and observe the state of deterioration of the coating film. In the observation, the ratio of the area of the portion where the blister is generated in the coating film to the whole is determined. ○ 5 when the rate is less than 5%
2020% was evaluated as Δ, and when it exceeded 20%, evaluated as ×.

The pitting corrosion test is similar to the iron dissolution test.
After soaking for a period of time, the state of corrosion was examined. The tip of the needle is 1.5 μmR,
The pressing load is 17g weight, the corrosion liquid is citric acid 1.5%, salt 1.
It was a 5% aqueous solution. In this test, corrosion occurs as if holes were dug along the flaw. This is shown in FIG. (A) Figure is a top view of the test piece after the test,
1 is a test piece, 2 is a flaw made by a needle, and 3 is a hole made by corrosion. It is determined that the shape of the hole 3 is such that the narrower the opening and the greater the depth, the greater the tendency of pitting corrosion.
(B) Diagram This is an enlarged schematic view of the hole 3, wherein the major axis and minor axis of the opening are a or b, the depth is d, and the tendency of pitting is 2d / (a + b), that is, the depth. And the average pore diameter of the opening. If this ratio exceeds 1.5, it is determined that the material is likely to cause pitting corrosion.

In the T-peel test, 50 mg / m ² of an epoxy phenol resin was applied to the treated surface, baked at 205 ° C. for 10 minutes, and thermocompressed with a nylon film interposed between the two coated test pieces cut to a width of 5 mm. The test piece was used as a measurement specimen, and the force required to peel it off at 20 μm / min was measured.

The weldability was evaluated by measuring the contact electrical resistance between the same type of materials. ^Two test pieces were stacked and inserted between copper electrodes having a diameter of 5 mm, and a current was applied under a pressure of 4000 kg / cm ² , and a contact resistance was determined from a current flowing at this time and a potential difference between the test pieces.

 Table 1 shows the test materials and test results.

In Examples, in the test No. 3 in which the amount of Cr and Ni is smaller than the preferable range, the iron elution amount is slightly larger, and in the test No. 7 in which the chromate layer is slightly smaller than the preferable range, the T-peel test value is slightly smaller. Conversely, in Test No. 10, in which the chromate layer was larger than the preferred range, the contact resistance was slightly large, but satisfactory results were obtained in all items including these.

In contrast, in the comparative example, the test with a small amount of Ni plating was performed.
In test No. 11, the contact resistance value was large and the weldability was inferior, and in the test with a small amount of Cr / Ni thermal diffusion layer, test No. 12 was inferior in post-working corrosion resistance, corrosion resistance under the coating, iron dissolution test, and had a large tendency to pit .
In Test No. 13 with a small chromate layer, the T-peel value was small, and in Test No. 14 with too many chromate layers, the contact resistance was large and the weldability was poor, and the test No. Even at .15, the contact resistance is large and the weldability is poor.

In the conventional example, the Cr plating layer is a non-diffusion layer and has a large tendency to pit. Inevitably, the corrosion resistance after processing and the corrosion resistance under the coating film are inferior, and the Fe elution amount is large.

[Effects of the Invention] As described above, according to the present invention, a Ni plating layer exists on a Cr / Ni thermal diffusion layer, and a thin chromate layer covers the Ni plating layer. Therefore, in addition to the corrosion resistance of Ni and Cr / Ni alloys, the Cr / Ni thermal diffusion layer alleviates the sharp potential gradient between Ni and Fe to prevent pitting, and the Ni plating layer reduces the contact resistance. It lowers the weldability, and the chromate layer enhances paint adhesion. As described above, the effect of the present invention, in which the layers constituting the film exhibit their characteristics and satisfy various properties as a material for a welding can, even when the film is a thin film, is significant.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of pitting for explaining the tendency of pitting. 1 ... test piece, 2 ... flaw, 3 ... pitting corrosion.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-232296 (JP, A) JP-A-60-162791 (JP, A) JP-A-62-274091 (JP, A) JP-A-63-163 499 (JP, A) JP-A-1-195268 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C25D 5/14 C25D 5/26 C25D 5/50

Claims (6)

(57) [Claims] In 1. A surface layer Cr · Ni thermal diffusion layer of the steel sheet has a 0.05 g / m ² or more 1 g / m ² or less of the Ni plating layer on the diffusion layer,
A steel plate for a welding can having a chromate layer on the Ni plating layer. 2. The total amount of Cr and Ni in the Cr / Ni thermal diffusion layer is 0.02.
The steel sheet for a welding can according to claim 1, wherein the steel sheet has a g / m ² or more and 0.2 g / m ² or less. 3. The chromate layer is 5 mmg / m ² or more and 30 mmg in terms of Cr.
/ m ² or less welded steel sheet for cans according to claim 1, wherein. 4. A steel sheet before heat treatment is plated with a Cr / Ni alloy, and when the steel sheet is subjected to a heat treatment, a heat diffusion layer of Cr / Ni is formed. A method for producing a steel plate for a welding can, characterized by performing a treatment. Plate manufacturing method. 5. After plating the surface of the steel sheet before heat treatment with Cr.
A method for producing a steel sheet for a welding can, characterized by applying a Ni plating, generating a heat-spreading layer of Cr / Ni when heat-treating the steel sheet, performing temper rolling, applying a Ni plating, and then performing a chromate treatment. . 6. After plating Cr on the surface of the steel sheet before heat treatment.
When applying Ni ・ Fe alloy plating and performing heat treatment on this steel sheet
A method for producing a steel sheet for a welding can, characterized in that a Cr / Ni heat diffusion layer is formed, temper rolling is performed, Ni plating is performed, and then a chromate treatment is performed.